Remove config-default.h

This file was the default mbedtls configuration in the mbedtls-psa
fork. It is no longer relevant.

tests/scripts/test-ref-configs.pl

@@ -17,10 +17,6 @@ use warnings;
 use strict;
 
 my %configs = (
-    'config-default.h' => {
-        'opt' => '-f Default',
-        'compat' => '-m tls1_2 -V NO',
-    },
     'config-mini-tls1_1.h' => {
         'compat' => '-m tls1_1 -f \'^DES-CBC3-SHA$\|^TLS-RSA-WITH-3DES-EDE-CBC-SHA$\'',
     },